A type of endoprosthesis device, commonly referred to as a stent, is placed or implanted within a blood vessel for treating stenoses, strictures, or aneurysms in the blood vessel. These devices are implanted within the vascular system to reinforce collapsing, partially occluded, weakened, or abnormally dilated sections of the blood vessel. Stents also have been successfully implanted in the urinary tract or the bileducts to reinforce those body vessels.
One common procedure for implanting the endoprosthesis or stent is to first open the region of the vessel with a balloon catheter and then place the stent in a position bridging the weakened portion of the vessel.
Prior art patents refer to the construction and design of both the stent as well as the apparatus for positioning the stent within the vessel. One representative patent is U.S. Pat. No. 4,140,126 to Chaudhury which issued Feb. 20, 1979. This patent discloses a technique for positioning an elongated cylinder at a region of an aneurysm to avoid catastrophic failure of the blood vessel wall. The '126 patent discloses a cylinder that expands to its implanted configuration after insertion with the aid of a catheter.
A second prior art patent to Dotter, U.S. Pat. No. 4,503,569 which issued Mar. 12, 1985 discloses a spring detent which expands to an implanted configuration with a change in temperature. The spring stent is implanted in a coiled orientation and heated to cause the spring to expand.
U.S. Pat. No. 4,733,665 to Palmaz which issued March 29, 1988 discloses a number of stent configurations for implantation with the aid of a catheter. The catheter includes a mechanism for mounting and retaining the vascular prosthesis or stent, preferably on an inflatable portion of the catheter. The stent is implanted by positioning it within the blood vessel and monitoring its position on a viewing monitor. Once the stent is properly positioned, the catheter is expanded and the stent separated from the catheter body. The catheter can then be withdrawn from the subject, leaving the stent in place within the blood vessel.
One difficulty in implanting the prosthesis or stent devices of the prior art is the inability to partially position the stent within the blood vessel in an expanded form and determine the appropriateness of the insertion prior to withdrawal of the catheter that delivers the stent. As the stent expands into contact with the blood vessel, it is discharged or separated from the catheter. Removal of an improperly positioned stent must be done surgically by an attending physician. It is accordingly one object of the invention to achieve a stent delivery method and apparatus which allows the stent or prosthesis to be positioned within the blood vessel and the appropriateness of the positioning monitored prior to separation of the stent from the insertion catheter.